6A - Geometric Optics
44. Total Internal Reflection
6A44.1 Total Internal Reflection in Water
A beam of light shines onto a mirror in an aquarium. The mirror reflects the beam toward the surface, and the angle of the mirror can be adjusted gradually so that one sees refraction, refraction and partial reflection, critical angle, and total internal reflection. As the angle of the beam approaches the critical angle, one also sees dispersion as the refracted beam spreads into a spectrum on the screen.
[Set-Up Time: 20 min.]
6A44.2 Light Pipe, Fiber Optic Cables
A laser shines into a long, curled light pipe and emerges at the other end. Stranded fiber optic cable is also available.
[Set-Up Time: 5 min.]
60. Thin Lens
6A60.1 Optics "Blackboard"
A large magnetic board with a fixed source of parallel light rays can be used to demonstrate geometric optics. Components include: flat mirrors, curved mirrors, thin lenses, thick lenses, transparent rectangular solids, and a prism.
65. Thick Lens
6A65.1 Fresnel Lens
The flat plastic lens from the surface of an overhead projector can be used for comic effect when held directly in front of the speaker's face.
[Set-Up Time: 5 min.]
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6B - Photometry
10. Luminosity
6B10.30 Paraffin Block Photometer
Two light sources, one twice as strong as the other, are placed a meter apart. Two paraffin blocks with a sheet of aluminum foil sandwiched between them form a photometer; move the photometer between the light bulbs until the brightness on each half appears equal. One can extrapolate the inverse square law of luminosity.
[Set-Up Time: 10 min.]
30. Radiation Pressure
6B30.1 Radiometer (Not!)
The spinning radiometer used in 4B40.1 Radiation of Heat does not demonstrate radiation pressure, as often thought. Shining a flashlight on it will push the black sides of the vanes, rather than the reflective sides, indicating that the spinning is due to heating and expanding the very small amount of gas inside, and not due to momentum transfer of photons. The effect of radiation pressure is many orders of magnitude smaller and requires a much more sensitive measuring device to detect.
[Set-Up Time: 5 min.]
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6C - Diffraction
10. Diffraction Through Slits
6C10.1 Single Slit Diffraction
A glass slide containing a variety of single slits of different widths (as well as double slit and grating configurations) can be placed in front of a laser, and the diffraction pattern viewed on the screen.
[Set-Up Time: 5 min.]
20. Diffraction Around Objects
6C20.1 Poisson's Spot (Arago's Spot)
A small circular object is placed in front of a laser beam, and the diffraction pattern, with a bright spot in the very center of the shadow, is observed on the screen. Note: this is hard to see in a large class unless students are allowed to come closer to the screen.
[Set-Up Time: 10 min.]
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6D - Interference
10. Interference from Two Sources
6D10.1 Double Slit Interference
A glass slide containing a variety of double slits of different widths and separations (as well as single slits and grating configurations) can be placed in front of a laser, and the interference pattern viewed on the screen.
[Set-Up Time: 5 min.]
See also: 3B60.1 Beats with Tuning Forks.
20. Gratings
6D20.1 Interference with a Grating
A glass slide with a variety of different grating configurations can be placed in front of a laser, and the interference pattern viewed on the screen.
(see images above in 6D10.1)
30. Thin Films
6D30.1 Newton's Rings
A convex lens held against flat glass is placed in the way of a beam of light. The reflected light shows circular interference fringes due to the varying thickness of the air gap between the pieces of glass.
[Set-Up Time: 10 min.]
Setup: 
Display on Screen: 
6D30.2 Soap Film Interference
White light is reflected off of a thin film of soap, showing black at the thinnest part and different colors at other parts of the film of different thickness. The film gradually gets thinner until it pops.
[Set-Up Time: 25 min.]
Setup: 
Display on Screen: 
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6F - Color
30. Dispersion
6F30.1 White Light and Prism
A beam of white light shining on a prism produces the rainbow spectrum on a screen.
[Set-Up Time: 10 min.]
Display on Wall: 
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6H - Polarization
10. Dichroic Polarization
6H10.1 Light Beam and Three Polaroid Filters
Send a light beam through a single polaroid filter (with a large arrow indicating the polarizing axis), then use a second polaroid filter to show that the beam is now polarized, and can be completely blocked if the second polarizer is set perpendicular to the first. Insert a third polarizer between the two, and show that some of the light beam is restored.
[Set-Up Time: 5 min.]
20. Polarization by Reflection
6H20.1 Brewster's Angle
There is no standard demo for this, but it can be done either by reflecting a light beam off a metallic sheet and examining the reflected ray with a polaroid filter, or by polarizing a laser beam, reflecting it off a glass surface, and rotating the angle of incidence until the reflected ray disappears.
[Set-Up Time: Unknown]
30. Circular Polarization
6H30.1 Polarization and Karo Syrup
Place a large polaroid sheet on the overhead projector, and place a bottle of karo syrup on top. View this through a second large polaroid sheet held in front.
[Set-Up Time: 10 min.]
6H30.2 Rotation by Sugar Solution
A light beam passes through one polaroid filter, then through a long tube filled with a sugar solution, and through a second polarizer. Moving the tube in and out of the path of light and changing the angle of the second polarizer shows that the polarization is rotated by the sugar.
[Set-Up Time: 20 min.]
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